This invention relates to load sensing apparatus and more particularly to a dual range force transducer for measuring compressive or tensile loads.
In many laboratory and commercial applications, it is desirable or necessary to measure either compressive or tensile forces. These forces may vary over a wide range and it may be necessary to have accurate measurements at both ends of the range. For example, it is desirable to know the magnitude of the brake drag for a dynamometer. Under heavy braking, loads as great as 3,000 pounds or more may be exerted by the brake. In order to measure these forces, a 5,000 pound strain gauge might be used. However, when the brakes are allowed to only drag, a force of perhaps only 20 pounds may be exerted. In order to measure this force using a 5,000 pound strain gauge transducer, the output of the transducer must be highly amplified. In view of the high amplification, the system is subject to error due to electrical noise both from the amplifier and from other nearby electrical equipment such as motors, relays, switches, brushes, etc. A low capacity transducer, such as a 50 pound strain gauge transducer for measuring a 20 pound load, is not susceptible to electrical noise of this type since its output need not be highly amplified. However, the large capacity transducer is required to measure the stopping torques present in the dynamometer.